Roadmap to Improving Quality of Optical Elements using d’Polariscope

Photoelastic fringes using Polariscope

With the growing use of precision moulded components in diverse fields ranging from optics to medical to microfluidics, there is a need to characterize and test them for birefringence or residual stress which would hinder their performance. It is well-known that a polariscope can be used for visualizing the residual stress in such materials. However, analysis is subjective at best and needs an experienced engineer.

d'Polariscope and Software

At d’Optron, we developed a real time quantitative d’Polariscope which provides birefringence and residual stress distribution over a field of view of 100 mm x 100 mm. The system also provides direction of the fast axis which corresponds to the direction of principal stress in the material.

The fringe pattern on the top right shows laser spot damage created by ultra-short pulses of different durations and number of shots. The butterfly pattern is the stress pattern generated by the spot which is barely visible.

The pattern on the bottom right is the residual stress developed below a glass surface due to polishing. Provides an indication of sub-surface damage during the process of glass polishing.

Applications for Birefringence Measurement and Si-wafer damage

Injection molded optical flats post UV curing process

The d’Polariscope has been widely used for testing of molded optics whether by injection molding or by thermal curing. The system can measure the average birefringence over the desired region of interest which can be used to qualify the optic for its desired application. Below are some examples of injection molded precision optical flat as well as ophthalmic lens which has been cured using UV curing process.

Birefringence in Micro-wells | Damage in Si-wafer

Tests were also conducted on micro-wells from different suppliers at the request of our client to see which showed minimal birefringence for their applications. A typical result from one such sample is shown to the extreme left.

The d'Polariscope can be modified to inspect damage and sub-surface defects in Si-wafer (Ref. 3). Similar to the glass sample shown above, butterfly fringes indicating damage in wafers can be seen in the picture to the right